1. Field of the Invention
The present invention relates to shaping the backs of book blocks, preparatory to the application of a cover thereto during the production of books, and particularly to forming the back of a book block which has previously been rounded such that the block assumes a shape which is appropriate to the binding to be applied thereto. More specifically, the present invention is directed to apparatus for controllably applying shaping forces to a book block back and especially to apparatus for providing a joint fold in a book block adjacent a rounded back thereof. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
2. Description of the Prior Art
This invention relates to an operation, performed during the manufacture of books, known in the trade as "backing". The preparation of a book block for receiving a cover is performed by rounding and backing apparatus which serially act on the block. The backing apparatus of the prior art include a shaped part, known as a backing bar, which moves backwards and forwards over the entire breadth of the book block back. As a result of this reciprocating movement, which is accompanied by the application of pressure and thus the generation of frictional forces, the outer edge regions of the folded printed sheets which comprise the book block are turned away from the center of the book block and are bent over towards the sides of the book block at angles which progressively increase from the block center towards the sides. The backing method and apparatus thus results in the book block receiving a generally mushroom-like back shape. It is necessary that the thus shaped book block back be stable, i.e., the printed sheets must be treated such that they will retain the desired shape which has been imparted thereto by the backing apparatus.
A book rounding and backing machine with a reciprocating shaped part which acts on the book block back, this machine being exemplary of the prior art, is shown and described in German Patent 1,536,507. Among other deficiencies, the apparatus disclosed in this German patent has limited operational speed due to the fact that the shaped part acts on the left and right sides of the book block alternatively.
At the conclusion of a backing operation a book block back should have a rounded shape with a multiplicity of radii. In order to impart this desired back shape to a book block, the shaped parts employed in the backing operation must be matched to the back radius desired for the print run in question. This requirement results in long machine set-up times, especially in high-output book production units, due to the difficulty of gaining access to the shaped parts for the purpose of removal and reinstallation. Long set-up time is becoming increasingly intolerable, particularly in view of the fact that there is a tendency in the book-making industry for the number of copies produced per print run to be reduced. It is also to be noted that the changing of the shaped parts, particularly the rounding bars of prior art backing apparatus such as exemplified by German Patent 1,536,507, requires highly trained personnel and necessitates the maintenance of a substantial inventory of different size bars. Both of these requirements contribute to significantly increased production costs.
Even when employing the best available prior art apparatus, as a result of the powerful recovery forces exerted by some papers, "backed" book blocks sometimes fail to retain the shape imparted thereto by the backing apparatus. This failure to retain shape is usually characterized by "sagging" of the back, usually in its central region. Such "sagging" results in unacceptable product and thus also has a deleterious effect on the cost of production of a book.